DE 197 11 589 A1 discloses a filter element, a slotted tube filter element in particular, with support rods around which is wound at least one wire profile in individual turns. Slots are left clear through which a fluid may pass. The profile is welded at least in part to the support rods. Filter elements such as this are readily obtainable on the market in both cylindrical and conical form. These filter elements are used, among other applications, in so-called reversible flow filter devices. Such devices have a filter inlet and a filter outlet for the fluid to be filtered. Fluid flows from the interior outward, or from the exterior inward subsequently for a reversible flow process. The respective fluid flows may also be provided in the reverse order for filtration and reverse flow for special areas of application.
One end of each rod support is inclined at an angle to the longitudinal axis of the filter element. The turns of the respective wire profile decrease in diameter in the direction of the sloped ends of the support rods to achieve the conical design of the respective filter element. The fluid intake area in the element is very large. The distance between the filter elements, if such elements are used in the reversible flow filter device described, increase in the direction of the outlet side of the housing. In this manner, the fluid is subjected to lower resistance on emerging from the interior of the respective filter element than in cylindrical elements. Accordingly, the pressure differential or the pressure as a whole decreases, a favorable situation from the viewpoint of the energy balance. In addition, constant flow of fluid is achieved during reverse flow. Flow at a constant rate is favorable in cleaning of the filter elements and gentle in operation of the reversible flow filter device.
The support grid structure, along with the wound-on wire profile, is enclosed on the outer circumference in a correspondingly conical screen grid for production of the conventional slotted tube filter element. The screen grid may be wound in strips around the wire profile, with the individual turns of the sieve filter connected to each other. The connection with the wire profile itself is produced by welded seams. The production process involved is costly. Moreover, the screen grid does not always come into direct contact with the wire profile. This process accordingly adversely affects filtration output and, on the whole, the rigidity of the entire filter.